Ticket #47608 - change slapi_entry_attr_get_bool to handle "on"/"off" values, support default value
    
    Description: Adding an API slapi_entry_attr_get_bool_ext, which is an
    extension of slapi_entry_attr_get_bool.  The difference is slapi_
    entry_attr_get_bool_ext returns the given default value if the type
    is not found in the entry.
    
    https://fedorahosted.org/389/ticket/47608
    
    Reviewed by rmeggins@redhat.com (Thank you, Rich!!)